Hard to find them selling individually, just like most haunted hats, demand is much bigger than supply.

http://www.tf2outpost.com/trade/10435998 Offer of 1 key + 2 ref for the spy set (Other items are ~1.66 together, making it 1 key + .33)

http://www.tf2outpost.com/trade/10415662 Offer of a key

http://www.tf2outpost.com/trade/10489105 3 willing buyers at 1 key

http://www.tf2outpost.com/trade/10079705 Buying for 1 key, only 1 add in 3 weeks

http://www.tf2outpost.com/trade/10651455 Buying for 4.33, new

http://www.tf2outpost.com/trade/10580503 Unbought at 4 ref for 3 days with autobump

http://www.tf2outpost.com/trade/10540829 Unbought at Backpack.tf prices for 4 days with autobump